Auto merge of #79349 - Nemo157:issue-79201, r=jyn514

Apply `doc(cfg)` from parent items while collecting trait impls

Because trait impls bypass the standard `clean` hierarchy they do not participate in the `propagate_doc_cfg` pass, so instead we need to pre-collect all possible `doc(cfg)` attributes that will apply to them when cleaning.

fixes #79201

2 files changed, 32 insertions, 6 deletions

diff --git a/src/librustdoc/clean/inline.rs b/src/librustdoc/clean/inline.rs
index f3067360f06..cef0e36505c 100644
--- a/src/librustdoc/clean/inline.rs
+++ b/src/librustdoc/clean/inline.rs
@@ -339,9 +339,6 @@ crate fn build_impl(
         return;
     }
 
-    let attrs = merge_attrs(cx, parent_module.into(), load_attrs(cx, did), attrs);
-    debug!("merged_attrs={:?}", attrs);
-
     let tcx = cx.tcx;
     let associated_trait = tcx.impl_trait_ref(did);
 
@@ -435,7 +432,7 @@ crate fn build_impl(
 
     debug!("build_impl: impl {:?} for {:?}", trait_.def_id(), for_.def_id());
 
-    ret.push(clean::Item::from_def_id_and_parts(
+    let mut item = clean::Item::from_def_id_and_parts(
         did,
         None,
         clean::ImplItem(clean::Impl {
@@ -450,7 +447,10 @@ crate fn build_impl(
             blanket_impl: None,
         }),
         cx,
-    ));
+    );
+    item.attrs = merge_attrs(cx, parent_module.into(), load_attrs(cx, did), attrs);
+    debug!("merged_attrs={:?}", item.attrs);
+    ret.push(item);
 }
 
 fn build_module(cx: &DocContext<'_>, did: DefId, visited: &mut FxHashSet<DefId>) -> clean::Module {
diff --git a/src/librustdoc/passes/collect_trait_impls.rs b/src/librustdoc/passes/collect_trait_impls.rs
index 4c3defabc32..1e9bc67de04 100644
--- a/src/librustdoc/passes/collect_trait_impls.rs
+++ b/src/librustdoc/passes/collect_trait_impls.rs
@@ -5,6 +5,7 @@ use crate::fold::DocFolder;
 
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
+use rustc_middle::ty::DefIdTree;
 use rustc_span::symbol::sym;
 
 crate const COLLECT_TRAIT_IMPLS: Pass = Pass {
@@ -90,7 +91,32 @@ crate fn collect_trait_impls(krate: Crate, cx: &DocContext<'_>) -> Crate {
         for &impl_node in cx.tcx.hir().trait_impls(trait_did) {
             let impl_did = cx.tcx.hir().local_def_id(impl_node);
             cx.tcx.sess.time("build_local_trait_impl", || {
-                inline::build_impl(cx, None, impl_did.to_def_id(), None, &mut new_items);
+                let mut extra_attrs = Vec::new();
+                let mut parent = cx.tcx.parent(impl_did.to_def_id());
+                while let Some(did) = parent {
+                    extra_attrs.extend(
+                        cx.tcx
+                            .get_attrs(did)
+                            .iter()
+                            .filter(|attr| attr.has_name(sym::doc))
+                            .filter(|attr| {
+                                if let Some([attr]) = attr.meta_item_list().as_deref() {
+                                    attr.has_name(sym::cfg)
+                                } else {
+                                    false
+                                }
+                            })
+                            .cloned(),
+                    );
+                    parent = cx.tcx.parent(did);
+                }
+                inline::build_impl(
+                    cx,
+                    None,
+                    impl_did.to_def_id(),
+                    Some(&extra_attrs),
+                    &mut new_items,
+                );
             });
         }
     }